Infusion of therapeutic fluids to treat patients is commonly used in hospitals and other medical care settings. Some infusions are carried out by hanging a bag or container of a fluid source on a pole above the patient so that fluid flows under the force of gravity through a length of tubing and into the vessel of a patient, and can be regulated by a user-controllable flow restrictor. In other instances, the flow of fluid into the patient is under the control of a programmed infusion pump located in the fluid pathway. The infusion pump is located in the fluid pathway such that a portion the container and infusion line is positioned above, or upstream, of the infusion pump.
Infusion pumps are ‘displacement regulation’ devices which permit precise control of the flow of a supply fluid, such as a medication, into the patient. For example, using an infusion pump, relatively precise amounts of fluid are infused at one or more specified flow rate. Moreover, the infusion pump may be programmed to change the rate of fluid flow during the infusion. This capability is useful where a primary fluid source, containing a first supply fluid, and a secondary fluid source, containing a second supply fluid, is coupled to the infusion pump. The infusion pump may be programmed to direct fluid to the patient at an initial rate when the second fluid is flowing to the pump, and then alter operation to direct fluid to the patient at a different rate when the second fluid is nearly empty and the first fluid begins to flow toward the pump.